1. Field of the Invention
The present invention relates to an image forming apparatus and a method of driving and controlling a head.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, or a combined machine thereof, an ink jet recording device is known, which is an image forming apparatus of a liquid ejection and recording system, using a liquid ejection head that ejects a liquid droplet as a recording head, for example.
Among such image forming apparatuses, an image forming apparatus is known, which includes a head drive control unit configured to generate a drive waveform including a plurality of drive pulses in time series, to select one, or two or more drive pulses from the drive waveform according to a droplet size, and to provide the selected drive pulses to a pressure generation unit.
In the liquid ejection head, a water repellant film is formed on a nozzle surface on which a nozzle for ejecting liquid droplets is formed in order to obtain a stable droplet ejection characteristic. However, when unevenness or deviation is caused in distribution of wettability in the vicinity of the nozzle, or an ink is solidified in the vicinity of the nozzle, due to abrasion or exfoliation of the water repellant film, a meniscus formed in the nozzle at meniscus oscillation becomes uneven, and the ink droplet ejected through the nozzle is more likely to bend.
Especially, immediately after a large droplet or a middle droplet having a large droplet size is ejected, the meniscus overflows in the vicinity of the nozzle, and the first liquid droplet ejected next tends to easily bend. When the droplet bending is generated, the image quality is decreased.
Therefore, conventionally, a configuration is known, in which an ejection pulse including a drive pulse that contributes to formation of a droplet having a plurality of droplet sizes is generated, a plurality of drive pulses that contributes to the formation of a droplet of a drive waveform includes a drive pulse including a waveform component that allows a pressure liquid chamber to be expanded and pulling in the meniscus in at least two stages just before allowing the pressure liquid chamber to be contacted and liquid droplets to be ejected, and the drive pulse has a time interval Is between an expansion start point of the pressure liquid chamber in a first stage and an expansion start point of the pressure liquid chamber in a second stage that satisfies a relationship of 0.3Tc≦Ts≦0.7Tc (Japanese Laid-open Patent Publication No. 2011-062821).
Further, a configuration is known, which includes a waveform component that makes the droplet speed of a satellite droplet higher than that of a main droplet in order to reduce the satellite droplet (Japanese Laid-open Patent Publication No. 2012-192710).
However, including of a waveform component that suppresses ejection bending in all pulses makes the overall drive waveform length longer and high frequency driving difficult.
Therefore, to obtain a desired maximum drive frequency, it can be considered that a part of the pulses does not include the waveform component that suppresses the ejection bending.
However, when a plurality of pulses are sequentially provided, a plurality of droplets is ejected in order, and a large droplet is formed, a droplet ejected by a pulse not including a waveform component that suppresses the ejection bending has problems of being subject to influence of remaining oscillation by a pulse provided before the droplet is ejected, and falling in a state of easily bending.
Therefore, there is a need to suppress an increase in waveform length of a drive waveform while suppressing ejection bending, and to make high frequency driving possible.